His directive is a remnant of that pre-1960 practice which seeks to "avoid scandal" by depriving divorced Catholics of the Eucharist.
There is NO BASIS for that prohibition, anywhere in Church law.
You might read Canon 1152, paying particular attention to the last Sentence, as well as Paras 2 & 3. The law on the topic of separation darn near MANDATES a discussion with the parish priest.
Your claim that one who is "unaware of serious sin" is to continue sacramental life is correct. But the Canon indirectly suggests, rather strongly, that there are reasons to visit with the pastor...